Swash plate variable capacity compressors used in air conditioning systems for automobiles or other applications comprise: a rotary shaft, which is rotatably driven by the rotating force of the engine; a swash plate, connected to the rotary shaft so that the tilt angle is variable; a piston for compression, connected to the swash plate; and other components. The tilt angle of the swash plate is varied, whereby the stroke of the piston is varied and the amount of the coolant gas discharged is controlled.
The tilt angle of the swash plate can be continuously changed by appropriately controlling the pressure in the control chamber (crank chamber) housing the swash plate and adjusting the state of balance between pressures applied to both surfaces of the piston, using a capacity control valve, which is driven so as to open or close by an electromagnetic force, while utilizing the intake pressure of an intake chamber for drawing in coolant gas, the discharge pressure of a discharge chamber for discharging the coolant gas pressurized by the piston, and the control chamber pressure in the control chamber.
A known capacity control valve of such description is one comprising, as shown in FIG. 5: discharge-side channels 73, 77, 74 interconnecting the discharge chamber and the control chamber; a first valve chamber 82 formed partway along the discharge-side channels; intake-side channels 71, 72, 74 interconnecting the intake chamber and the control chamber; a second valve chamber (actuation chamber) 83 formed partway along the intake-side channels; a valve body 81 formed so that a first valve part 76, which opens/closes the discharge-side channels 73, 77, 74 and which is arranged in the first valve chamber 82, and a second valve part 75, which opens/closes the intake-side channels 71, 72, 74 and which is arranged in the second valve chamber 83, integrally perform a reciprocating motion and perform a mutually opposite opening/closing action; a third valve chamber (capacity chamber) 84 formed partway along the intake-side channels 71, 72, 74 nearer the control chamber; a pressure-sensitive body (bellows) 78, which is arranged in the third valve chamber, exerts an urging force in an extending (expanding) direction, and contracts with an increase in surrounding pressure; a valve seat body (engaging part) 80, which is provided to the free end, in the direction of expansion/contraction, of the pressure sensitive body, and which has an annular seat surface; a third valve part (open-valve connection part) 79, which integrally moves with the valve body 81 in the third valve chamber 84 and which can open or close the intake-side channels by engaging with or detaching from the valve seat body 80; a solenoid S for exerting an electromagnetic driving force on the valve body 81; and other components (hereafter referred to as “prior art;” e.g., refer to Patent Reference 1.)
In this capacity control valve 70, even if a clutch mechanism is not provided to the variable capacity compressor with regards to capacity control, if there is a need to change the control chamber pressure, the discharge chamber and the control chamber can be interconnected and the pressure Pc in the control chamber (control chamber pressure) can be adjusted.
Specifically, as shown by a dashed line in FIG. 6, if there is an increase in the cooling load during cooling, the electromagnetic driving force increases, and a force acts so as to reduce the degree of opening of the first valve part 76 (see dash-single-dot line at the bottom left in FIG. 6). When the degree of opening of the first valve part 76 is reduced, the amount of coolant flowing into the crank chamber decreases, the pressure in the crank chamber decreases, and the tilt of the swash plate (angle with respect to a plane perpendicular to the drive shaft) increases. Meanwhile, if the cooling load is small, the electromagnetic driving force decreases, and a force acts so as to increase the degree of opening of the first valve part 76 (see dash-double-dot line at the top right in FIG. 6), the amount of coolant flowing into the crank chamber increases, the pressure in the crank chamber increases, and the tilt of the swash plate decreases.
If the control chamber pressure Pc increases while the variable capacity compressor is in a stopped state, the third valve part (open-valve connection part) 79 and the valve seat body (engaging part) 80 detach. When the solenoid S is switched on and the valve body 81 is activated in this state, the intake-side channels are opened and the intake chamber and the control chamber are interconnected.
A swash plate variable capacity compressor comprising the above capacity control valve 70 is “externally” controlled, where the intake pressure is controlled according to an external signal. Since the valve body 81 has a high actuation response, when the electromagnetic force is reduced and the first valve part 76 is opened, there is a tendency for the valve to open at high speed, the amount of coolant flowing into the crank chamber to increase rapidly, and the sensitivity to the rise in pressure in the crank chamber to also increase (see dashed line in FIG. 6). If the sensitivity to the rise in pressure in the crank chamber increases excessively, there may be instances in which the discharge capacity decreases excessively, the action of the valve body 81 becomes unstable, resulting in unstable phenomena such as “hunting.” This tendency is more likely to occur if the valve body 81 has a high actuation response. With regards to air conditioning control using an automotive air conditioning device in which this swash plate variable capacity compressor is used, hunting may not only be accompanied by temperature fluctuation in the vehicle chamber, adversely affecting air conditioning control, but may cause torque fluctuation in the compressor, adversely affecting the engine.